"unspecified" in the standards sense of "unspecified behavior", i.e. any chosen behavior is permissible. The compiler doesn't have to document the behavior and the behavior isn't constrained, it just isn't undefined. That's still better than where we are today.
I looked this up after you mentioned it upthread, I thought you meant implementation-defined, but I learned that yeah, this exists too. The difference is that implementation-defined requires documentation of the choice made, whereas unspecified does not. However,
> the behavior isn't constrained
C++23, at least, does say
> The range of possible behaviors is usually delineated by this document.
